In the manufacture of molded records, such as conventional audio records and the more recently developed video discs, a plastic material is molded between a pair of metal parts known as stampers. Stampers are thin metal discs which have formed in the molding surface thereof a surface relief pattern which includes an information track containing signal elements corresponding to the program desired to be reproduced on playback of the molded record.
The stampers are the final product of a multi-step replication process which is referred to in the art as matrixing. The initial step in the matrixing process is to cut the required surface relief image into a flat, disc-shaped member known as a recording substrate. The information track portion of the surface relief pattern is cut into the recording substrate in the form of a spiral which is essentially concentric with the center of the recording substrate. It is important that the information track be as concentric as possible with the center of the recording substrate, and that all subsequent replicas produced in the matrixing process have the information track positioned concentrically in order to eliminate run-out and other related problems in the molded records.
After the surface relief pattern is cut into the recording substrate, the recording substrate is replicated by electrodepositing a metal, such as nickel, on the surface of the recording substrate. When a predetermined thickness of metal, typically about 9 mils (2.4 mm), has been deposited on the substrate, the resulting electroformed part, called a master, is then carefully separated from the surface of the recording substrate.
The resulting master is then in turn used as a matrix, i.e., a part on which a replica is to be formed. A metal, again typically nickel, is electrodeposited on the surface of the master until a predetermined thickness of metal, typically about 9 mils of an inch (2.4 mm), is deposited on the matrix. The resulting replica formed on the matrix, which is referred to as a mold, is then carefully separated from the surface of the master.
The mold in turn is then used as a matrix on which to form additional replicas. A metal, such as nickel, is electrodeposited on the mold until typically about 7 mils of an inch (1.8 mm) thickness of metal has been electrodeposited on the mold. The resulting electroformed replica which is the stamper must then be carefully separated from the mold and is thereafter used to mold records as noted above.
For purposes of simplifying the further explanation of the present invention, the term "matrix" will be used hereinafter unless otherwise indicated to refer to a part which is to be replicated, and the term "replica" will be used hereinafter unless otherwise indicated to refer to a part which is to be formed on the matrix. It should be noted that the replicas formed in one step of the matrixing process are thereafter used as the matrixes in the subsequent step in the matrixing process.
One of the major problems encountered in the matrixing process is the separation of the electroformed replicas from the matrixes on which they are formed. In the conventional separation methods employed in the art, the outer edge of the sandwich comprised of the matrix and the replica electroformed on the matrix is split at the edges of the replica by using a sharp blade or the like. This initial step breaks the surface bond at the outer edge between the matrix and the replica. Thereafter, a portion of the outer edge of the replica is bent upward and gripped with pliers or the like, and the replica is stripped from the surface of the matrix. The separation step under the best of conditions is somewhat erratic and uncontrollable, as sometimes the replica and matrix will easily snap apart from each other and at other times they are extremely difficult to separate. The separation process often results in the replica or the matrix being bent or otherwise irreparably damaged.
Some attempts have been made to apply a separation force at the center hole portion of the sandwich comprised of the replica and the matrix in order to separate the replica from the matrix. Attempts have been made, for example, to cut and split the replica from the matrix at the center hole with a tool similar to that used in the technique employed at the outer edges. Attempts have also been made to inject gases or fluids at the center hole portion between the matrix and the replica to force the replica from the matrix. The above-noted attempts and other similar attempts have not, however, proven to be completely satisfactory in that it is still difficult at best to induce separation at the center hole when using conventional electroforming methods to form the replicas on the matrix. The center hole which is obtained using conventional electroforming methods is inherently relatively small, rough, and irregular in configuration so that it is difficult to get a reliable grip at the center hole portion of the replica.
A further problem that is encountered in the matrixing process is centering of the electroformed matrixes on the cathode heads used in the electroforming process. The typical ragged-edged, irregularly-shaped center holes in the electroformed parts obtained using conventional matrixing processes makes it difficult, if not impossible, to accurately center the electroformed parts thereafter used as matrixes on the cathode heads. The inability to accurately center the matrixes in the matrixing process causes considerable complications in the final processing of the stampers and also can lead to related problems, such as excessive run-out and the like in the molded records.
What would be highly advantageous would be a method for improving the separation of electroformed replicas from matrixes and also for improving the centering of matrixes in the electroforming process.